Let us illustrate by considering a few methods of rather restricted application. We are often aided in the solution of a problem by asking its opposite. If we ask ourselves “What constitutes gracefulness?” we may find ourselves at a loss for suggestions, because gracefulness always seems “so natural.” But if we ask its opposite, “What constitutes awkwardness?,” suggestions are more apt to occur. If we find, for instance, that awkwardness consists in undue bodily effort in making a movement, we may assume that gracefulness consists in ease of movement. In the same way the question of what makes us forget may be helped by asking ourselves what makes us remember, and light may be thrown on the causes of success in business and in life by a study of the causes of failure. The method of analogy likewise encourages suggestions. Analogy consists in noting certain likenesses between things, and assuming that they also possess other common qualities. Striking use of analogy is made in dealing with the planet Mars. At each pole there are great white patches. The size of these varies markedly with the seasons, which suggests that like the earth, Mars has great areas of ice and snow at its two poles which melt and re-form. The general surface is reddish, but three-eighths of it is covered by blue-green tracts, and these are usually inferred to be seas. These again are connected by an intricate system of blue-green lines, which some scientists believe to be canals, but on this there is much controversy. In Mars we have at once an illustration of the possibilities and dangers of analogy. In the whole discussion of constructive method thus far, I have left out the two most common and useful methods of all. The first of these we may designate by a somewhat formidable title: _empirical observation_. Empirical, at least for our present purposes, means merely that which comes within experience. But the term is generally opposed to scientific. Thus Dewey gives an example: “A says, ‘It will probably rain to-morrow.’ B asks, ‘Why do you think so?’ And A replies, ‘Because the sky was lowering at sunset.’ When B asks, ‘What has that to do with it?’ A responds, ‘I do not know, but it generally does rain after such a sunset.’ He does not perceive any _connection_ between the appearance of the sky and the coming rain; he is not aware of any continuity in the facts themselves—any law or principle, as we usually say. He simply, from frequently recurring conjunction of the events, has associated them so that when he sees one he thinks of the other.”[5]